WK 2 - C2 - Quality Assurance in Hematology and Hemostasis Testing
primary standard
a material of known, fixed composition that is prepared in pure form, often by determining its mass on an analytical balance.
"pre-pre" analytical variables
laboratory assay utilization and physician test ordering patterns.
Manufacturer specificity data
transferred from the package insert to the laboratory validation report
Sample
A data series that represents a single population, for instance, a series of prothrombin time results from a population.
True negative
Assay correctly excludes a disease or condition in those without it.
True positive
Assay correctly identifies a disease or condition in those who have it.
False negative
Assay incorrectly excludes disease or condition when it is present
False positive
Assay incorrectly identifies disease or condition when none is present.
Laboratory-developed assay
Assays devised locally ("home-brew"); FDA evaluates using criteria developed for FDAapproved or cleared assay kits.
Calibration Verification
Controls are used independently of the calibration process so that systematic errors caused by deterioration of the calibrator or a change in the analytical process can be detected through internal quality control.
Prepare new control and reassay
Controls may deteriorate over time when exposed to adverse temperatures or subjected to conditions causing evaporation
Recalibrate instrument
Instrument may require repair
Accuracy
It is a measure of agreement between an assay value and the theoretical "true value" of its analyte
Modified approved assay
Local facility modifies an FDA-approved or cleared assay.
Research use only
Local facility performs all validation steps. Research use only assays are intended for clinical trials, and carriers are not required to pay. Local facility prepares an advance beneficiary notice to indicate patient may be required to pay
Analyte-specific reagent
Manufacturer may provide individual reagents, but not in kit form, and may not provide package insert validation data. Reagents are not promoted for use on specific instruments or in specific assays. Local facility performs all validation steps.
Publication of reports
Postanalytical Component: Laboratory Staff Responsibility: Are results accurately transcribed into the information system? Are they reviewed for errors by additional laboratory staff? If autoverification is in effect, are the correct parameters employed? Do reports provide reference intervals (RIs)? Do they flag abnormal results? Are result narratives appended when necessary? Does the laboratory staff conduct in-service education to support test result interpretation? Are critical values provided to nursing and physician staff? Are verbal reports confirmed with feedback? Are anomalous findings resolved?
Timeliness
Postanalytical Component: Laboratory Staff Responsibility: Are turnaround times recorded and analyzed? Are laboratory reports being posted to patient charts in a timely fashion?
patient satisfaction
Postanalytical Component: Laboratory Staff Responsibility: Does the institution include laboratory care in patient surveys? Was specimen collection explained to the patient?
Test request forms
Preanalytical Component: Laboratory Staff Responsibility: Are requisition forms legible? Can the phlebotomist confirm patient identity? Are physician orders promptly and correctly interpreted and transcribed? Is adequate diagnostic, treatment, and patient preparation information provided to assist the laboratory staff to appropriately test and interpret results?
Specimen Management
Preanalytical Component: Laboratory Staff Responsibility: Are specimens centrifuged correctly? Are tests begun within specified times? Are specimens and aliquots stored properly? Are coagulation specimens consistently platelet-poor?
Specimen transport
Preanalytical Component: Laboratory Staff Responsibility: Are specimens delivered intact, sealed, and within specified time limits? Are specimens maintained at the correct temperature?
Test orders
Preanalytical Component: Laboratory Staff Responsibility: Conduct continuous utilization reviews to ensure that physician-generated orders are comprehensive and appropriate to patient indications. Inform physician about laboratory test availability and ways to avoid unnecessary orders. Reduce unnecessary repeat testing.
Stat orders and timeliness
Preanalytical Component: Laboratory Staff Responsibility: Do turnaround time expectations match clinical necessity and ensure that stat orders are reserved for medical emergencies? Does laboratory management meet established turnaround time requirements?
Specimen collection
Preanalytical Component: Laboratory Staff Responsibility: Is the patient correctly identified, prepared, and available for specimen collection? Is fasting and therapy status appropriate for the assay? Is the tourniquet correctly applied and released at the right time? Are venipuncture sites appropriately cleansed? Are timed specimens collected at the specified intervals? Are specimen tubes collected in the specified order? Are additive tubes properly mixed? Are specimen tubes labeled correctly?
Positive predictive value (PPV)
Proportion with a disease who have a positive test result compared with all individuals who have a positive test result
Diagnostic sensitivity
Proportion with the disease who have a positive test result
Negative predictive value (NPV)
Proportion without a disease who have a negative test result compared with all individuals who have a negative test result
Diagnostic specificity
Proportion without the disease who have a negative test result
Prepare fresh reagents and reassay
Reagents may have evaporated or become contaminated.
Analytical specificity
The ability of an assay to distinguish the targeted analyte from interfering substances within the specimen matrix is called
FDA-approved or cleared assay
The local facility may use package insert data for linearity, interferences, and specificity but must establish clinical accuracy and precision.
Noise
This cutoff prevents false-positive results generated by low-end assay interference
Distribution of proficiency materials to all sites
What process ensures comparability in multi-site validation?
Reassay
When a limit of 62 SDs is used, 5% of expected assay results fall above or below the limit.
Area under the curve
When performing a receiver operating curve analysis, what parameter assesses the overall efficacy of an assay?
Student t-test
Which is a statistical test that compares means?
Control
You purchase a preserved whole blood specimen from a distributor who provides the mean values for several complete blood count analytes. What is this specimen called
Proficiency testing
You require your laboratory staff to annually perform manual lupus anticoagulant profiles on a set of plasmas with known values. This exercise is known as
ROC (Receiver Operating Characteristic) curve
a further refinement of diagnostic efficacy testing that may be employed to determine the decision limit (cutoff, threshold) for an assay when the assay generates a continuous variable.
Bland-Altman difference plot
also known as the Tukey mean-difference plot, provides a graphical representation of agreement between two assays.
Validation
an activity comprised of procedures to determine accuracy, specificity, precision, limits, and linearity
screening test
an assay that is applied to a large number of subjects within a convenience sample where the participant's condition is unknown.
"post-post" analytical variables
appropriate application of laboratory assay results
Calibrators
are assayed by a reference method in expert laboratories, and their assigned value is certified
Proficiency testing systems
are available from external quality assessment agencies, and proficiency reports are made accessible to laboratory assessors.
aliquots
are often called survey or proficiency testing specimens and include preserved human donor plasma and whole blood, stained peripheral blood films and bone marrow smears, and photomicrographs of cells or tissues
Levey-Jennings chart
assumes that the control results distribute in a Gaussian manner and provide limits at 1, 2, and 3 SD above and below the mean.
U.S. Food and Drug Administration (FDA)
categorizes assays as cleared, analyte-specific reagent (ASR) assays, research use only (RUO), and laboratory-developed (home-brew) assays.
Standard deviation (SD),
commonly used measure of dispersion, is the square root of the variance and is the mean distance of all the data points in a sample from the sample mean.
delta check system
compares a current analyte result with the result from the most recent previous analysis for the same patient.
Incidence
describes the number of events occurring within a randomly selected number of subjects representing a population, over a defined time.
Prevalence
describes the total number of events or conditions in a broadly defined population, for instance, the total number of patients with chronic heart disease in the United States
lower limit of detection
determined from the computed standard deviation.
Moving average systems
do not replace the use of control specimens but provide additional means to detect shifts and trends.
Variance
expresses the deviation of each data point from its expected value, usually the mean of the data series (sample) from which the data point is drawn.
External quality assessment
further validates the accuracy of hematology and hemostasis assays by comparing results from identical aliquots of specimens distributed at regular intervals among laboratories nationwide or worldwide.
Regression analysis
gains sufficient power when 40 or more patient specimens are tested using both the new and reference assay in place of or in addition to calibrators.
moving average concept
has been generalized to WBC and platelet counts and to some clinical chemistry analytes, albeit with moderate success.
Dr. James Westgard
has established a series of internal quality control rules that are routinely applied to long-term deviations, called the Westgard rules.
Diagnostic efficacy testing
includes determination of diagnostic sensitivity and specificity, positive and negative predictive value, and receiver operating characteristic analysis.
Alternative (Research) Hypothesis
logical opposite of the null hypothesis.
New or modified assays
may also be compared to reference methods.
Specimen
may be defined as a single data point within a data series.
Intercept
measures constant systematic error (or bias, in laboratory vernacular), a constant difference between the new and reference assay regardless of assay result magnitude
Slope
measures proportional systematic error; the higher the analyte value, the greater the deviation from the line of identity
Paired t-test
new and reference assays are performed using specimens from the same donor (aliquot).
reject null hypothesis
p ≤ 0.05 (5%) or p ≤ 0.01 (1%)
Power
p, means Probability that the test is able to detect an effect. (Ranges from the scale of 0-1).
Standard t-test
population distribution is normal (Gaussian), SDs are equal and, assays are independent
Quality control
processes are employed to document assay validity, accuracy, and precision, including external quality assessment, reference interval preparation and publication, and lot-to-lot validation.
Dr. Brian Bull
proposed a method of employing patient RBC indices to monitor the stability of hematology analyzers, recognizing that the RBC indices mean cell volume (MCV), mean cell hemoglobin (MCH), and mean cell hemoglobin concentration (MCHC) remain constant on average despite individual patient variations.
Controls
provide known values and are sampled alongside patient specimens to accomplish within-run assay validation.
Control manufacturers
provide limits; however, local laboratory practitioners must validate and transfer the manufacturer limits or establish their own, usually by computing standard deviation from the first 20 control assays
North American Specialized Coagulation Laboratory Association
provides survey systems for specialty coagulation laboratories in the United States and Canada and is affiliated with the ECAT (external quality control of diagnostic assays and tests, ecat.nl) Foundation External Quality Assessment Program of the Netherlands, which provides survey materials throughout Europe
Validation
recorded on standard forms available from commercial sources, for example, Data Innovations LLC EP Evaluator.
moving average method
requires a computer to calculate the averages, does not detect within-run errors, and is less sensitive than the use of commercial controls in detecting systematic shifts and trends.
Null Hypothesis
states that there is no difference between or among the means or variances of the populations being compared.
Analytical specificity
the ability of an assay to distinguish the analyte of interest from anticipated interfering substances within the specimen matrix.
Linearity
the ability to generate results proportional to the calculated concentration or activity of the analyte.
Quality assurance
the broader concept, encompassing preanalytical, analytical, and postanalytical variables
mode
the data point that appears most often in the sample.
median
the data point that separates the upper half from the lower half of a data series (sample).
Precision
the expression of reproducibility or dispersion about the mean, often expressed as SD or CV%, as discussed in a subsequent section.
geometric mean
the n root of the product of n individual data points and is used to compute means of unlike data series.
coefficient of variation (CV)
the normalized expression of the SD, ordinarily articulated as a percentage (CV%).
AMR or Analytical Measurement Range
the range of results a method produces without any specimen pre-treatment, such as dilution, and is similar to a linearity study
Arithmetic mean (𝑥̅), or average
the sum (o) of the individual data values divided by the number (n) of data points
Action limits
vary by laboratory, but many managers reject the new lot when more than one specimen (data point pair) generates a variance greater than 10% or when all variances are positive or negative.